1. Field of the Invention
The present invention relates to a camera having automatic focus adjusting function in which lens for focus adjustment is driven to an in-focus point corresponding to a result of focus detection. More specifically, the present invention relates to a camera having automatic focus adjusting apparatus suitable for a single lens reflex camera.
2. Description of the Related Art
A camera having automatic focus adjustment function of interest to the present invention is disclosed in Japanese Patent Laid Open Number 62-125311/1987. According to this article, a prediction correction is proposed in which the lens is driven in association with a speed of an object when a presently detected direction of defocus is the same as that direction detected last time. However, whether the prediction correction is to be carried out or not is not decided depending on a photographing mode such as a continuous photographing mode and a single photographing mode in the prior art. Meanwhile, in a camera employing a continuous photographing mode capable of continuously taking photographs of a plurality of frames per second, employment of a continuous AF mode has been proposed, in which the lens is continuously driven to the position of an object corresponding to the result of present focus detection during taking photographs. When this continuous AF mode is employed, a release priority AF mode is also used in most cases, in which a request for releasing is given priority to a request of focusing.
A camera having automatic focus adjusting function exhibits a drawback that focusing precision in taking a photograph of a moving object is lower than the focusing precision in taking a photograph of a static object. The reason for this is that the object moves away from the in-focus position before the shutter is actually released, even if the lens is driven to the presently detected in-focus point to carry out the releasing operation. In view of the foregoing, prediction correction has been proposed as in the above mentioned prior art, in which, if the presently detected defocus direction is the same as the last defocus direction, it is determined that the object is moving and the lens is driven in correspondence with the speed of the object.
However, there is various errors and the fluctuations in the results of focus detection of the focus detecting apparatus. If there is an error in detecting focus in the same direction in taking photographs of a static object, it is erroneously determined that the object is moving. Consequently, the lens may possibly be driven based on the error of the focus detecting apparatus. Therefore, it is not very effective to constantly carry out determination of whether prediction correction is to be carried out or not. Whether the prediction correction should be carried out or not should preferably be determined only under such photographing condition that there is a high possibility of the object moving.